Try this: While driving relatively fast so you hear the "howl" pretty good, do a weight transfer left and right to see if the howl changes pitch or goes away. The left-right weight transfer will unload the wheel that has the bad bearing and make the noise dissipate, in general. If you quickly turn left and noise disappears, it's the right wheel bearing that is bad... and vice versa. If both are bad, well, the noise won't go away totally, but it might change pitch/sound so that you know which of the two bearings is "worse off". Give that a shot.

On on open highway with nobody nearby, just doing this across a couple of quick-left-then-right sharp freeway lane changes should tell you something. Quick left/right alternating back and forth and listen for sound changes.